Why have lectures in the information age?

Inertia/tradition accounts for many things. "Doing things they way they've always been done" [sic] is usually considered defensible, too. Also, people have already-existing mental models for what a lecture should be like, often including specifics about the subject matter.

The fact that information is available on-line is not wildly different from the fact that information was available in universities' libraries. Yes, a sufficiently motivated person can simply go to the internet/library and find lots of information. A potential problem is that there is too much information, that it is fundamentally chaotic (despite our attempts to impose order or develop "search engines"), and fundamentally hard for a non-expert to evaluate. Even worse, a non-expert may fail to realize that they are failing to correctly evaluate information. :)

Still, yes, very many classes/lectures are boring, and attendance is often easily replaced by reading the designated textbook or other sources. However, in several decades of observation, many students (at all levels) either prefer or have become accustomed to a kind of passivity, so that they'd rather show up somewhere at a regularly scheduled time, see their fellow students, and have the pace and content dictated to them by even a fairly boring lecturer.

In my own student days, I did not like going to classes, for the obvious sorts of reasons: for one thing, if one had read the book, a slo-mo flawed, re-recital of it seems pointless in comparison to just re-reading at one's own speed. Second, if one found the material interesting, why stop? Why not read ahead? Why not look at other sources, too, for complementary viewpoints? Why not look at related stuff? (This was as feasible in libraries as it is on the internet, with perhaps two added advantages: there really was not much junk in libraries, since it was filtered, and, second, the chances of serendipitous discoveries in libraries was larger than on the internet.) Such a process inevitably makes the "canned" lectures seem crazily irrelevant.

(Also, years ago, libraries were some of the few reliably air-conditioned places!)

But let's ignore the problem of student passivity, and ask why/how a lecture _could_be_ better than just reading a book or searching on the internet. Arguably, a lecture is not better if it just amounts to reading from the book, copying from it onto a blackboard, etc. I would claim that trying to make lectures simply present text-book material is a big mis-use of the medium! That is, systematic presentation of all the details belongs in a book or on-line, but not in a lecture. Oppositely, what could be in a lecture that could not be in a book or notes? "Affect", meaning intonation, gestures, facial expressions, theatrical effects, and so on, are hard to put into writing, but (by "lecturers" capable of it) can be put into a lecture. This includes reaction to facial expressions and body language of the audience/students, and conversational interaction if the group isn't too large. For example, lectures can include "pep talks" that would be hard to fit into writing. "Reassurance" can be done live better than in writing, I think.

Another feature is the "live/real-time" aspect: a lecturer (in mathematics, my field, for example) can literally do things in the lecture room, live, in real time, with voice-over narrative, in effect. That is, the audience can witness the genuine activity as exercised by an expert practitioner, with accompanying critical and methodological comments. Yes, up to a point, textbooks and monographs could be written in such a fashion, but it seems that stylistic pressures move them in the opposite direction, aiming for a sort of artificial perfection that can only be achieved by much editing! Too often it seems that writing aims to create impressive edifices rather than be accessible, helpful ... and a live lecturer can easily do better, if they try.

So, for my own lecturing, I definitely do think in terms of "adding value" beyond what students could derive from written sources, and in terms of using the medium in ways that distinguish it from static written sources (and not having a lecture be a bad re-copying of those written sources).

I think the first critical false premise in your question is the notion that lectures are not frequently used outside of academia. Speaking as somebody who sees quite a bit of both academia and industry, as well as some of the government and amateur communities, I would say that the lecture is used nearly universally in every domain where one person is trying to convey information to a large group of people at the same time.

This is not to say that a lecture is always the right choice. There are, as you point out, a lot of different ways of conveying information and many of them are useful in the university setting as well. Flipping the classroom, for example, is something that many schools are experimenting with at all levels. That very overabundance of information that you point out as a value, however, is also a problem that a well-done lecture can solve.

Here is what a lecture does that is unique: within the sea of related information, a good lecture shows which exactly are the conceptual elements that a particular expert believes are most important about a topic, and then shows a well-developed way of understanding how they relate to one another. The format may be anything from chalk to powerpoint to documentary movie, and many good lectures incorporate elements of audience participation and embedded example problems to help further stimulate learning. In every case, however, the distinguishing feature of a lecture is that the class turns over its collective attention to direction by a single expert, and the way in which that attention is directed is a significant part of the value.

While jakebeal's answer is excellent, I will add just two more points.

Some university educators simply do not understand pedagogy very well. That is, they spend their time improving their knowledge of their specific domain and do not focus on improving their knowledge about how to best facilitate student learning. Some educators also make the mistake thinking that their students have the same ability to "drink from a firehose" and if they just deliver the most important content then the students will be able to sort it out in their out-of-class studying. In that regard, a 1-2 hour lecture might save a student 10 hours of research time, especially if the student is unfamiliar with research (like a first or second year undergraduate). As pointed out in the answer I already referenced, these lecturing sessions could be recorded and moved out of the classroom (flipping), providing more time for discussion in class.

Lastly, and this partially repeats the sentiments of jakebeal, lecturing is great at some things. For example, I have some classes where we meet in two sessions per week. The first session is a lecturing session where I introduce them to some of the most important ideas they should be aware of. They are expected to then take those ideas, and do some research, applying the concepts to the real world. Then, the next session, is more of a seminar with much higher levels of interaction without any lecturing.

So, lecturing can be done for the wrong reasons but it also has its place.